Patent Document 1 discloses an engine arranged to switch between a first driving method (for example, homogeneous combustion) on a high rotation and high load side, and a second driving method (for example, stratified charge combustion) on a low rotation and low load side on which a fuel economy efficiency is higher than that of the first driving method. A depression force control device according to Patent Document 1 is configured to immediately increase a depression reaction force (depression force) of an accelerator pedal when a driving region of the engine enters a boundary driving region just before switching to a first driving region when the driving region of the engine is switched from a second driving region in which the second driving method is performed to the first driving region in which the first driving method is performed. The increase amount of the depression force is canceled when the driving region of the engine is returned from the boundary driving region to the second driving region.
The device according to Patent Document 1 is configured to increase the depression force of the accelerator pedal. The device is further configured to release the increase amount by using, as a boundary, the above-described boundary driving region for decreasing the fuel consumption rate. The accelerator pedal is a main operation member for driving the vehicle as intended by the driver. An operation feeling which the driver experiences and the operational effects with respect to a feeling of drivability of the vehicle are very important for assessment of the quality of the entire vehicle. In the practical application of such a device, which may contribute to the decrease of the fuel economy, it is necessary to balance the fuel economy reduction and the operability of the accelerator pedal or the operability of the vehicle at a high level.
For example, if the depression force control device is structured such that the depression force of the accelerator pedal can be varied by driving an actuator, it is conceivable that the control is performed so that a driving command value to this actuator is set to be once increased to be more than a target value, and to be returned to the target value. Thus, the driver feels the sudden increase of the depression force which is performed when the driving region enters from the second driving region to the boundary driving region when the driver depresses the accelerator pedal so as to improve the response of the depression force increase.
However, there may also be other cases in which the control is performed so that the driving command value to the actuator is set to be once increased to be more than the target value, and to be returned to the target value. In such cases, if the controlled variable of the driving command value with respect to the target value is not appropriately set, the depression force of the accelerator pedal becomes excessively large. Consequently, there is a problem that the operability of the accelerator pedal is deteriorated.